Starter devices of the type concerned here are mostly configured with a handle in order to start the internal combustion engine manually. The handle comprises a grip, which is connected with a pulling element such as a cord or a flat band, with the cord or flat band being wound around the pulling medium roller. When the user exerts a pulling force on the pulling medium, the pulling medium roller is set in rotation.
The rotation is transferred to the crankshaft of the internal combustion engine by means of a functional connection with the crankshaft in such a manner that the internal combustion engine can start. In addition to manual actuation of the starter devices, electric motors are known, which set a drive element in rotation, which is in functional connection with the crankshaft. Furthermore, other mechanical, hydraulic or pneumatic starter devices are known, which however all function according to the same basic principle. Consequently, the kick starter for mopeds can likewise be designated a starter device to which the present invention applies.
Owing to the construction of the internal combustion engine, the rotation of the crankshaft has a torque profile which varies periodically. During the compression phase of the internal combustion engine cycle, a high torque is required, which must be passed to the crankshaft in order to set the internal combustion engine in rotation.
During the expansion phase, the crankshaft in contrast only requires a low torque or no torque at all, since the expansion of the gas in the combustion chamber of the internal combustion engine produces the effect of a gas spring so that the crankshaft rotates automatically. This highly periodic torque requirement of the internal combustion engine to be started produces in the pull cord a correspondingly periodic rising and falling force requirement, which the user must apply. The user senses this periodic rising and falling force requirement as a jerky, pulsing load.
Force peaks can be avoided with a variokinematic connection or mechanism between the cord roller and the crankshaft, as is disclosed in the earlier filed application DE 20 2007 006 551.5. The damping effect is however rather small, since there is no appreciable flexibility in the functional connection. The effect of the different phase positions between the crankshaft and the pulling medium roller can however be compensated by using variokinematic connections.
In order to damp the force peaks which reach the pulling medium roller via the crankshaft, torsion spring devices are likewise known, which are arranged between the pulling medium roller and a driver. The rotation brought about by means of the pulling medium and the pulling medium roller is passed via the torsion spring device so that the torsion spring device makes possible a compensation of the rotation for the compression phases of the internal combustion engine which causes the engine shaft to lead. The force peaks in the cord pull, which would otherwise arise as a result of two components with opposed acceleration vectors meeting each other are thereby effectively suppressed. The torque required for starting is transferred in a form-fitting manner via large-area stops positioned on the outside of the torsion spring. The disadvantage here arises in the case of pulling medium rollers consisting of a plastic material having a tendency to wear as a result of the high surface pressures from the torsion spring element.